1. Field of the Invention
The present invention relates to a sample analyzer for analyzing the composition of a sample by emitting accelerated light ions such as helium (He) or hydrogen (H) onto the sample to determine the energy spectrum of ions scattered resulting from elastic collisions with elements in the sample.
2. Description of the Related Art
Attention is being given to sample analyzers of a type that analyzes the composition of samples by measuring the energy spectrum of ions elastically scattered. Examples of such a sample analyzer include Rutherford backscattering spectrometry (RBS) which utilizes ions with high energy over 300 KeV.
The RBS can analyze the composition of a plurality of elements in a sample through measurement of the energy spectrum of scattered ions at various detection angles θ.
A high resolution Rutherford backscattering spectrometer, described in “Kobe Steel Engineering Report” Research and Development Division, Kobe Steel Ltd., vol. 52, pp 53–56 can analyze the composition of samples with high depth resolution. More specifically, ions with single energy such as He or H are emitted onto a sample and the ions are elastically scattered by the elements in the sample. An electromagnetic spectrometer deflects the scattered ions having an energy spectrum in a magnetic field. The deflected energy spectrum is measured by a semiconductor ion detector.
The basic operation of a high resolution Rutherford backscattering spectrometer Y utilizing the aforementioned electromagnetic spectrometer will now be described in reference to FIGS. 6A and 6B. An ion source (not shown) in an accelerator 119 emits ion beams horizontally, and an E×B filter 117, where an electric field and a magnetic field are orthogonal to each other, selects monovalent helium ions out of the ion beams, for example. The E×B filter 117 deflects the trajectories of divalent helium ions, hydrogen atom ions, and hydrogen molecule ions, and a slit 107 eliminates these ions. The selected monovalent helium ions converge through a magnetic quadrupole lens (not shown) and are led into a chamber or vacuum container 103 to be emitted onto the surface of a sample 102 (not shown) from a horizontal direction, the sample 102 being supported by a goniometer 109. Then, the ion beams are elastically scattered by elements at the surface of and the inside of the sample. Part of the scattered ion beams enters an electromagnetic spectrometer 104 disposed in the vicinity of the chamber 103, and the trajectories of the ion beams are deflected through a magnetic field and are detected by an ion detector 108.
The electromagnetic spectrometer 104 includes a magnetic yoke, a pole piece, and an exciting coil, which are not shown in the drawing, and is rather large in size and weight. Since the exciting coil will heat up, the electromagnetic spectrometer 104 is normally disposed outside the chamber 103. The electromagnetic spectrometer 104 spectroscopically analyzes the ion beams elastically scattered by the elements of the sample in the chamber 103, and the ion beams having an energy spectrum are led into the ion detector 108. The energy distribution of the ion beams elastically scattered at the surface of the sample differs depending on the thin film structure of the sample such as elements on the surface or their composition, depth or position. Therefore, detection of the scattered ion beams by altering the detection angle θ (a scattering angle θ from the surface of the sample) can selectively analyze the thin film structure of the surface of the sample. Accordingly, in order to detect the ion beams at different detection angles θ, a plurality of detection ports with different detection angles θ is disposed on the circumferential surface of the chamber 103 in the known high resolution Rutherford backscattering spectrometer. The electromagnetic spectrometer 104 can be connected to the plurality of detection ports.
Japanese Unexamined Patent Application Publication No. 2002-237271 discloses another type of sample analyzer. A magnetic pole is disposed inside a vacuum container, and an exciting coil is disposed outside the vacuum container. Magnetic yokes are also provided inside and outside the vacuum container and lead a magnetic flux generated by the exciting coil to the magnetic pole, which is isolated by the wall of the vacuum container from the exciting coil. Both an analysis of the magnetic field and detection of the energy spectrum of the scattered ions can be performed in the vacuum container where a sample is disposed. Accordingly, the analyzer can be miniaturized and an adverse effect of heating exciting coil on the analysis can be avoided.
Furthermore, an ion beam analyzing apparatus described in the U.S. Pat. No. 5,350,920 is also known as a sample analyzer utilizing ion beams.
According to the aforementioned high resolution Rutherford backscattering spectrometer, the electromagnetic spectrometer can be connected to a plurality of detection ports. However, the electromagnetic spectrometer needs to be attached to another detection port in order to change the detection angle of the scattered ions. Accordingly, the electromagnetic spectrometer has to be detached from a chamber or a bracket when attaching the electromagnetic spectrometer to another detection port. This is troublesome and also deteriorates the efficiency of the analysis.
Furthermore, when the electromagnetic spectrometer is detached from the chamber, the interior of the chamber is exposed to atmospheric air. Thus, after the electromagnetic spectrometer is attached to another detection port, the chamber has to be put back into a vacuum. Every time the electromagnetic spectrometer is attached to another detection port, the vacuum is broken in the chamber. Therefore, a long time is required in order to exhaust air in the chamber. Furthermore, when the sample is an ultra-thin film, exposure of the surface of the sample to air incurs contamination.
With all the aforementioned known analyzers, a plurality of beamline components such as a filter or a slit are disposed between the accelerator 119, which includes the ion source and an accelerating duct, and the chamber 103. To facilitate adjustment of the beamline components, the accelerator 119, the beamline components, and the chamber 103 are disposed in a line and ion beams are horizontally emitted from the accelerator 119 onto the sample. Alternatively, the directions of ion beams emitted vertically from the accelerator 119 are bent by, for example, a bending magnet so that the ion beams propagate horizontally. The sample is irradiated with the bent ion beams from a horizontal direction through the beamline components.
Although there has been a demand to analyze a large wafer in recent years, not a single known analyzer satisfies the demand. One of the reasons is that a wafer is inserted from a vertical direction with all the known analyzers and thus a large wafer cannot keep itself leveled when inserted. Another reason is that even if a wafer can be inserted while keeping itself leveled, a sample stage has to be rotated from a horizontal position to a substantially vertical position so that the ion beams are horizontally emitted on the wafer. However, keeping a large wafer in a substantially vertical position is unstable, resulting in breakage and contamination of the wafer. Furthermore, a chamber that can hold and rotate a large wafer is disadvantageously complicated. Accordingly, when a large wafer is a subject, it is preferred that a sample be placed laterally on a sample stage and ion beams be emitted vertically onto the sample.